(From memory) The date format is associated with the regional settings from the blog. You can change that in blog settings. I believe the setting you choose on initial install is dominant, so you may also check one of the conf files.

Excuse me for replying without adding value, but way back when this was a problem that was solved. I apologize for no details, but if one searches the forums for maybe "long date format" one might find the solution that worked back then.

It is also possible I'm dreaming the solution exists/existed, but for sure the "long date" problem has been identified previously. Perhaps it's time to pull out the "rarely used but very effective" call to a developer?

I love you I love you I love you! You're great you're great you're great! Oh the pain oh the pain oh the pain!